Britain on Monday warned it could fine TikTok £27 million ($29 million) over a potential failure to protect children's privacy on the Chinese-owned video app.
The Information Commissioner's Office said the social media company "may have processed the data of children under the age of 13 without appropriate parental consent".
The ICO also found that the short-form video platform may have "failed to provide proper information to its users in a concise, transparent and easily understood way".
The watchdog has served the group with a notice of intent -- which is a legal document that precedes a possible fine -- over the possible breach of UK data protection law.
"We all want children to be able to learn and experience the digital world, but with proper data privacy protections," said Information Commissioner John Edwards.
"Companies providing digital services have a legal duty to put those protections in place, but our provisional view is that TikTok fell short of meeting that requirement."
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In response, TikTok said it disagreed with the ICO's provisional views and stressed that no final conclusions had been reached.
"While we respect the ICO's role in safeguarding privacy in the UK, we disagree with the preliminary views expressed and intend to formally respond to the ICO in due course," TikTok said in a statement.